Range extension for optical fiber sensing systems

Abstract

An optical fiber sensing system includes a sensing optical fiber and one or more optical amplifiers in series with the sensing fiber and arranged to increase the power of sensing pulses travelling along the fiber to thereby increase the range of the sensing system. The optical fiber sensing system is one selected from the group including an optical fiber distributed acoustic sensor (DAS), an optical fiber distributed temperature sensor (DTS), or an optical time domain reflectometry (OTDR) system.

Description

TECHNICAL FIELD[0001]The present invention relates to optical fiber sensing systems, such as optical time domain reflectometers (OTDRs), as well as optical fiber distributed acoustic sensors (DASs), and optical fiber distributed temperature sensors (DTSs). Specifically, the present invention provides for range extension of such sensing systems by providing for optical signal repeater or amplifier modules to increase the power of any sensing pulses sent down the optical fiber.BACKGROUND TO THE INVENTION AND PRIOR ART[0002]Optical fiber based sensing systems are known already in the art. OTDRs are used to determine fiber condition and properties, such as splice or connector losses and attenuation, whereas DAS and DTS systems use backscatter and / or reflections from along the fiber to sense acoustic energy incident on the fiber, or ambient temperature around the fiber, as appropriate. An example prior art DAS system is the Silixa® iDAS™ system, available from Silixa Ltd, of Elstree, UK,...

AI Technical Summary

Benefits of technology

The present invention is an optical fiber sensing system that uses repeater amplifiers to increase the range of the sensing system. Optical amplifiers, such as EDFAs, are placed in series with the sensing fiber to increase the power of sensing pulses sent in a forward direction along the fiber. Optical circulators are used to route backscattered and reflected light around the amplifier to increase the power of the backscatter. Signal conditioning circuitry can filter and reconstract the sensing pulse to make it more like the original pulse when output by the amplifier. The system can have multiple lengths of fiber connected together in series with amplifiers to further increase the range. The bypass optical componentry includes amplifiers to amplify the optical backscatter and maintain its spectral form. Pulse conditioning componentry can re-generate the optical pulse with an intended envelope to maintain sensing fidelity over a longer range. The optical amplifier can also reproduce the regenerated optical pulse at a different wavelength to improve signal discrimination.

Problems solved by technology

At present most optical fiber DAS and DTS systems are limited in range to around 5 km or so, due to attenuation in the fiber of both of the outward sensing pulse, and the resulting backscatter and / or reflections along the fiber.

Whilst range can of course be increased by the provision of several independent systems (i.e. it would be possible to position a DAS box every 5 km along a pipeline), such increases the system deployment cost, and leads to other problems in synchronisation of monitoring of several independent sensor systems of the same type.

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